JP2004126625A - Method for manufacturing double refraction film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a thin and light double refraction film capable of obtaining a liquid crystal display device of an STN type or the like with excellent contrast and visual field angle by an oriented film having optical rotatory power in addition to birefringence and capable of compensating even the twist of liquid crystal. <P>SOLUTION: In the method for manufacturing the double refraction film, the oriented film having the birefringence and the optical rotatory power is obtained by performing control to a film composed of polymer in different directions in a range where the angle change θ of the direction is indicated by an equation: 0+mπ<θ<90+mπ (where m is 0 or an integer ≥1) and performing two times or more of stretching processings. The double refraction film indicates characteristics that the chromaticity coordinates x,y form a circular track on a CIE chromaticity diagram in arranging it between two polarizing plates and rotating one polarizing plate, and the liquid crystal display device of the STN type or the like having an excellent achievement degree or the like of black-and-white display and color display by coloring prevention is obtained. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a method for producing a birefringent film having birefringence and optical rotation, which is useful for preventing coloration and improving contrast of a liquid crystal display device of STN type or the like.

Liquid crystal display devices that can be directly connected to IC circuits with low voltage and low power consumption focus on the variety of display functions and the possibility of weight reduction, and various screens of personal computers, word processors, data terminal devices, etc. In recent years, liquid crystal display devices of the STN type have become the mainstream in place of the TN type because of their excellent large-capacity display performance and high-speed response.

In the super twisted nematic (STN) type liquid crystal, the twist angle is larger than that in the TN type, so that the liquid crystal display image is colored in a blue or yellow system. In a black and white display, the contrast and visibility are reduced, and the color display is reduced. It is a cause of inhibition. Therefore, various coloring prevention means have been proposed.

Conventionally, a method using a retardation plate made of a stretched film has been proposed as the coloring prevention means. However, a conventional general retardation plate does not exhibit optical rotation, and can only deal with a phase difference due to birefringence, but has a poor effect of compensating for twist of a liquid crystal, and cannot deal with a high-contrast liquid crystal display device. .

As a birefringent film exhibiting birefringence and optical rotation, a stretched film composed of a half-wave plate or a stretched film imparted with optical rotation with a light-rotating substance has been known. However, the former has a drawback that the wavelength functioning as an optical rotator is substantially only monochromatic light, and the latter has a drawback that it is necessary to use an optical rotatory substance for imparting optical rotatory power.
JP-A-6-3525 JP-A-6-27319

The present invention obtains a stretched film having optical rotation in addition to birefringence and capable of compensating for liquid crystal twist, and obtains a thin and light liquid crystal display device such as an STN type display which is excellent in contrast and viewing angle. It is an object of the present invention to develop a method for producing a birefringent film that can be used.

According to the present invention, a polymer film is controlled in a different direction and an angle change θ in the direction in a range represented by the formula: 0 + mπ <θ <90 + mπ (where m is 0 or an integer of 1 or more). It is another object of the present invention to provide a method for producing a birefringent film, wherein a stretched film having birefringence and optical rotation is obtained by performing a stretching treatment two or more times.

According to the present invention, an optical rotation property can be imparted by a stretching treatment, a thin and light film having a birefringence and an optical rotation property can be compensated for a twist of a liquid crystal, and a birefringence which is easily manufactured from a stretched film and is easy to manufacture. A film can be obtained, which is arranged between two polarizing plates, and when one of the polarizing plates is rotated, its chromaticity coordinates x and y form a circular locus on the CIE chromaticity diagram. With the use of such a liquid crystal display device, it is possible to obtain an STN type liquid crystal display device which is excellent in the degree of achieving black and white display and color display by preventing coloring, contrast, viewing angle, and the like.

In the production method of the present invention, an angle change θ in a different direction and in a different direction on a film made of a polymer is represented by the formula: 0 + mπ <θ <90 + mπ (where m is 0 or an integer of 1 or more). A birefringent film made of a stretched film having birefringence and optical rotation is obtained by performing stretching treatment twice or more while controlling within the range.

施 す By performing the stretching treatment two or more times in the different directions, a stretched film having optical rotation in addition to birefringence can be obtained. This is because, in addition to the molecular orientation by the first stretching process, a new molecular orientation by the second and subsequent stretching processes in another direction is added, and another molecular orientation accumulated in the film by the stretching process in the different direction is performed. It is considered that the molecular orientation in the direction changes in the thickness direction of the stretched film based on the maximum direction of the refractive index, and the change in the direction of the molecular orientation causes optical rotation.

The birefringent film according to the present invention, that is, the stretched film having birefringence and optical rotation, has its chromaticity coordinate x when placed between two polarizing plates and one of the polarizing plates is rotated. , Y form a circular locus such as a circle or an ellipse on the CIE chromaticity diagram. FIG. 1 shows an example of the locus. An ellipse surrounding the chromaticity coordinate point of the light source shown inside the chromaticity diagram is an example of a circular locus.

に お い て In the above description, the locus of the chromaticity coordinates x, y can be obtained based on a known operation according to JIS Z 8701 or the like. That is, as shown in FIG. 2, for example, the birefringent film 1 is disposed between the C light source 11 composed of a halogen lamp, the polarizers 12 and 13 composed of a Glan-Thompson prism, and the polarizers 12 and 13 in an optical system composed of a photomultiplier 14. Then, one of the polarizers, for example, the polarizer 13 is rotated at a predetermined angle, for example, 10 degrees, and the spectral transmittance is measured at each angle, and the measured value is used in the XYZ color system based on the formula according to JIS {Z} 8701. The trajectory can be visualized by obtaining tristimulus values, calculating chromaticity coordinates at each rotation angle from the tristimulus values, and plotting the chromaticity coordinates on an xy chromaticity diagram.

延伸 Stretching of the polymer film in a different direction can be performed by an appropriate method such as uniaxial or biaxial. The addition of a new molecular orientation in another direction by the subsequent stretching process, while maintaining the molecular orientation by the preceding stretching process, is performed by setting the stretching temperature to be equal to or lower than the glass transition temperature of the polymer forming the film. It can be efficiently performed by a method in which a subsequent stretching treatment is performed at a stretching temperature lower than the stretching temperature, but is not limited to this method, and molecular orientation may be imparted by an appropriate method.

In the stretching process in the different direction, the angle change θ in the stretching direction in the subsequent stretching process as the different direction is represented by the formula: 0 + mπ <θ <90 + mπ (where m is 0 or an integer of 1 or more). It is controlled within the range. In the case of uniaxial stretching, a subsequent uniaxial stretching process is performed in a direction in which the angle change with respect to the previous stretching axis becomes 45 to 60 degrees, and a new molecular orientation different from the molecular orientation by the previous stretching process is added. However, a method of imparting properties showing birefringence and optical rotation is preferable.

Stretching in a different direction having an angle change θ in the stretching direction, which satisfies the above equation, effectively changes the maximum direction (molecular orientation) of the refractive index in the thickness direction of the film. This is more advantageous than efficiently giving the property. The birefringence, retardation, optical rotation and the like of the obtained stretched film can be controlled by changing stretching conditions such as stretching ratio and stretching direction.

製造 In the production of a stretched film, a stretching treatment can be carried out while adhering a heat-shrinkable film, if necessary. In normal stretching such as uniaxial or biaxial, the molecules are oriented in a direction substantially parallel to the film surface, but in the stretching process under heat-shrinkable film bonding, the molecules are oriented in a direction inclined to the film surface. You can also. Therefore, the direction of molecular orientation in the stretched film may be parallel to the film surface or may be inclined.

ポ リ マ ー As the polymer forming the birefringent film (stretched film), an appropriate polymer capable of forming an optically transparent film can be used. Preferably, it is a polymer having a large intrinsic birefringence value and capable of forming a homogeneous film by solution casting. The polymer can be used in an appropriate form such as a homopolymer, a copolymer, a derivative thereof, or a blend.

ポ リ マ ー Polymers that can be preferably used include, for example, polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyamide, polyimide, polyethersulfone and the like. Above all, a polycarbonate polymer, a polyarylate polymer, a polysulfone polymer, a polyester polymer, and the like can be particularly preferably used.

The preferred birefringent film is an achromatic color having a light transmittance of 70% or more. Further, when there is a possibility that molecular orientation may be relaxed by environmental conditions such as heat treatment as in a manufacturing process of a liquid crystal display device, etc., the glass transition temperature is 105 ° C. or more, especially 110 ° C. to prevent the relaxation. A birefringent film composed of a polymer having a temperature of at least ° C is preferred.

INDUSTRIAL APPLICABILITY The birefringent film according to the present invention can highly compensate optical characteristics due to twisting of liquid crystal and the like, and can compensate the visibility of a liquid crystal cell exhibiting birefringence and optical rotatory power such as STN type liquid crystal. . This is because the stretched film (birefringent film) has birefringence and optical rotatory power, and on the basis thereof, a circular locus on the CIE chromaticity diagram as in the case of the STN type liquid crystal illustrated in FIG. It is thought that this is due in particular to having optical rotation characteristics having a wavelength width as a color mixing system.

A conventional birefringent film having only birefringence and no optical rotation, such as a conventional uniaxially stretched film or a simultaneously or sequentially biaxially stretched film, has a locus on the CIE chromaticity diagram shown in FIG. It is a straight line. Therefore, it is considered that the fact that a circular locus is shown on the CIE chromaticity diagram is a characteristic based on having optical rotation in addition to birefringence.

The birefringent film according to the present invention is generally a single-layer stretched film obtained by stretching a single-layer film, but a single-layer stretched non-adhesive or adhesive multilayer film or It may be composed of a multilayer stretched film.

Therefore, the birefringent film may be composed of a single-layer stretched film, or may be formed as a superimposed product of the same or different films 15, 16 via the adhesive layer 2 as shown in FIG. The number of superpositions is arbitrary, and optical characteristics such as phase difference can be controlled by the number of superpositions and the arrangement angle of the optical axis. Note that the thickness of the birefringent film can be appropriately determined according to optical characteristics such as retardation. Generally, the thickness is 500 μm or less, especially 200 μm or less based on a single-layer film in terms of flexibility and the like.

Further, the birefringent film, in its practical use, for example, a different type of birefringent film such as a retardation film or a film for improving viewing angle characteristics molecularly oriented in the thickness direction, or other optical elements such as a protective film or a polarizing plate. One type or two or more types can be used in an overlapping manner. The combination of the superpositions can be appropriately determined according to the optical characteristics required for compensating the visibility of the liquid crystal display device and the like.

Incidentally, an elliptically polarizing plate can be formed by combining a birefringent film and a polarizing plate. FIG. 4 illustrates an elliptically polarizing plate obtained by laminating the birefringent film 1 and the polarizing plate 3 via the adhesive layer 2.

As the polarizing plate, an appropriate one such as a polarizing film can be used, and there is no particular limitation. In general, iodine and / or a dichroic dye is adsorbed and stretched on a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, and an ethylene / vinyl acetate copolymer-based partially saponified film. A polarizing film made of a polyene oriented film, such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride, is used. The thickness of the polarizing film is generally 5 to 800 μm, but is not limited thereto.

The polarizing plate may have a transparent protective layer on one or both sides of the polarizing film. As the material for forming the transparent protective layer, those having excellent transparency, mechanical strength, heat stability, moisture shielding property, and the like can be preferably used. Typical examples thereof include polymers such as polyester resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, acrylic resin, and acetate resin. The transparent protective layer can also serve as the birefringent film.

There is no particular limitation on the type of transparent adhesive or pressure-sensitive adhesive for bonding the birefringent films to each other or the polarizing plate and the like, but curing and drying are performed in order to prevent a change in the optical characteristics of each functional film. In this case, those which do not require a high-temperature process are preferred, and those which do not require a long curing treatment or drying time are desirable.

The elliptically polarizing plate has its birefringent film, polarizing plate or transparent protective layer treated with an ultraviolet absorber, for example, a salicylic acid ester compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound, a nickel complex salt compound, or the like. UV absorbing ability can be imparted by a method such as the following.

(4) In forming a liquid crystal display device, it is preferable to arrange the birefringent film according to the present invention between the liquid crystal cell and the polarizing plate from the viewpoint of compensating the visibility of the display device. FIG. 5 shows an example. 4 is a liquid crystal cell. The birefringent film is preferably disposed between the polarizing plate on one side or both sides of the liquid crystal cell.

Any liquid crystal cell can be used, but the birefringent film according to the present invention can be particularly advantageously used for a liquid crystal cell exhibiting birefringence and optical rotation such as STN type. The birefringent film that can be preferably used from the viewpoint of compensating the visibility and the like is one that compensates as much as possible the optical rotation type birefringence due to the liquid crystal cell. Thus, black-and-white display and color display with improved contrast and viewing angle characteristics by preventing coloring can be realized.

A 20% by weight methylene chloride solution of polycarbonate having a weight average molecular weight of 80,000 was cast on a stainless steel belt, dried until the residual volatile matter became 3%, and then peeled off, and a film obtained was uniaxially stretched at 158 ° C. Then, the film was uniaxially stretched again at 150 ° C. in a direction at 45 ° to the stretching axis to obtain a birefringent film comprising a stretched film having birefringence and optical rotation.

A 20% by weight methylene chloride solution of polycarbonate having a weight average molecular weight of 80,000 was cast on a stainless steel belt, dried until the residual volatile matter became 3%, and then peeled off, and a film obtained was uniaxially stretched at 158 ° C. Then, a punched film punched at an angle of 60 degrees with respect to the stretching axis is adhered and sandwiched with a heat-shrinkable film via an adhesive layer, rolled into a roll, and then uniaxially stretched at 153 ° C. The shrinkable film was peeled off to obtain a birefringent film composed of a stretched film having birefringence and optical rotation.

A 20% by weight methylene chloride solution of polycarbonate having a weight average molecular weight of 80,000 is cast on a stainless steel belt, dried until the residual volatile content becomes 3%, and then peeled off, and the obtained film is adhered with a heat shrinkable film. After heat-shrinkable film is peeled off from it after stretching uniaxially at 158 ° C, the resulting film is uniaxially stretched at 150 ° C in the direction of 60 ° to its stretching axis, and birefringent A birefringent film comprising a stretched film having properties and optical rotation was obtained.

Comparative Example 1
A 20% by weight methylene chloride solution of polycarbonate having a weight average molecular weight of 80,000 was cast on a stainless steel belt, dried until the residual volatile content became 3%, and then peeled off, and a film obtained was uniaxially stretched at 158 ° C. Thus, a uniaxially stretched film having birefringence but not optical rotation was obtained.

Comparative Example 2
A 20% by weight methylene chloride solution of polycarbonate having a weight average molecular weight of 80,000 was cast on a stainless steel belt, dried until the residual volatile matter became 3%, and then peeled off. ) Direction to obtain a biaxially stretched film having birefringence but not optical rotation.

Comparative Example 3
A 20% by weight methylene chloride solution of polycarbonate having a weight average molecular weight of 80,000 was cast on a stainless steel belt, dried until the residual volatile matter became 3%, and then peeled off. The film was biaxially stretched successively in the direction) to obtain a biaxially stretched film having birefringence but not optical rotation.

Evaluation test xy chromaticity diagram The birefringent film or uniaxially stretched film obtained in Examples and Comparative Example 1 was placed between polarizing plates in TFF-120AFT (manufactured by Oak Manufacturing Co., Ltd.), and the spectral transmittance was measured in a chromaticity measurement mode. did. In the measurement, one of the polarizing plates was set so that its absorption axis was at 45 degrees, the sample was set thereon so that the stretching axis was at 0 degrees, and the analyzer-side polarizing plate was set based on its absorption axis. The chromaticity was determined from the spectral transmittance at each set angle by rotating the lens at intervals of 10 degrees in the range of 0 to 180 degrees.

Ｘ The xy chromaticity diagrams prepared from the above results are shown in FIGS. 1 and 6 to 8. 1 shows the case of Example 2, FIG. 6 shows the case of Example 1, FIG. 7 shows the case of Example 3, and FIG. 8 shows the case of Comparative Example 1. According to each xy chromaticity diagram, in the case of the embodiment, and in the case of the one having birefringence and optical rotation, a circular locus is formed while the chromaticity coordinates x and y surround the chromaticity coordinate point of the light source. This can be seen from FIGS. 1, 6, and 7.

On the other hand, in the case of Comparative Example 1 consisting of a uniaxially stretched film, the locus in the case of having birefringence but not having optical rotation was found to be a straight line (FIG. 8).

相違 The difference in the results of the trajectory between the circular shape and the straight line is considered to be based on whether the birefringent film has optical rotation in addition to the birefringence. That is, according to the color polarization theory (for example, “Applied optics”, written by Hiroshi Kubota, published by Iwanami Zensho, p. 163) between the Nicols of the birefringent substance, the difference in the trajectory occurs based on the difference in the optical rotation. It can be estimated that.

Visibility As shown in FIG. 9, the birefringent film or uniaxially stretched film obtained in Example and Comparative Example 1 was arranged on the viewing side of an STN type liquid crystal cell in which chromaticity coordinates x and y showed a circular locus, A polarizing film (NPF-EG1225DU, manufactured by Nitto Denko Corporation) was set on both sides of the arrangement to form a liquid crystal display device, and the transmittance of light in a driven state and a non-driven state was measured, and the ratio was used as a contrast. Calculated. Further, the viewing angle at which the contrast becomes 5 or more was examined.

The results are shown in the following table.

Example 1 Example 2 Example 3 Comparative Example 1
Contrast 15 23 25 10
Viewing angle (degrees) -28 to 30 -37 to 50 -38 to 47 -25 to 27

From the table, it can be seen that a liquid crystal display device having excellent contrast can be formed by using the birefringent film according to the present invention. Further, as in a film stretched using a heat-shrinkable film, a higher degree of compensation can be achieved such that the viewing angle characteristic is improved as the locus of the chromaticity coordinates x and y approaches the locus of the liquid crystal cell. I understand.

The biaxially stretched films obtained in Comparative Examples 2 and 3 were also prepared with xy chromaticity diagrams according to the above, and applied to STN-type liquid crystal cells to check their visibility. Is a straight line as in the case of Comparative Example 1 in FIG. The contrast and the viewing angle of the visibility were almost the same as those of Comparative Example 1.

Xy chromaticity diagram of the birefringent film obtained in Example 2 Illustration of chromaticity measurement method Sectional view of an example of a superimposed birefringent film Sectional view of elliptically polarizing plate example Sectional view of liquid crystal display device example Xy chromaticity diagram of the birefringent film obtained in Example 1 Xy chromaticity diagram of the birefringent film obtained in Example 3 Xy chromaticity diagram of the uniaxially stretched film obtained in Comparative Example 1 Xy chromaticity diagram of STN type liquid crystal cell

Explanation of reference numerals

1, 15, 16: birefringent film 2: adhesive layer 3: polarizing plate 4: liquid crystal cell


Patent applicant Nitto Denko Corporation Daito Tsutomu Fujimoto

Claims (2)

In a film made of a polymer, an angle change θ in different directions and in the directions is controlled in a range represented by the formula: 0 + mπ <θ <90 + mπ (where m is an integer of 0 or 1 or more), and 2 A method for producing a birefringent film, wherein a stretched film having birefringence and optical rotation is obtained by performing a stretching treatment at least twice. In claim 1, when the stretched film is disposed between two polarizing plates and one of the polarizing plates is rotated, its chromaticity coordinates x and y have a circular locus on the CIE chromaticity diagram. A method for producing a birefringent film to be formed.

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